Sniper detection systems are used to detect the presence of a gun or rifle. Some current systems accomplish this by measuring the acoustic shockwave that occurs when the gun is fired using an array of sensors. One notable disadvantage of this technique is that the gun cannot be detected until it is fired, which increases the risk of danger to a human target. Other current systems can detect light reflected off of the optics in a gun scope; however, this technique cannot detect guns without scopes.
Another current technique proposes to use radio waves to detect the presence of objects based on the resonance properties of the object. For example, U.S. Patent Application Publication No. 2010/0079280 by Lacaze et al. discloses that a tailor-made signal can be configured to resonate with specific objects, such as the barrel cavity of a gun. The resonated signal is reflected to a receiver that processes the signal and attempts to identify the presence and type of weapon by comparison with a library of tailor-made signals that are known to produce such resonance in specific weapons. The technique disclosed by Lacaze only detects a weapon if the signal is specifically tailored to interact with the weapon so as to create a specific signature in the frequency domain; other objects are not detected.